T. rex’s older and equally sizable relative discovered in New Mexico

A partial skull once believed to be from a T. rex is a newfound species, a study revealed. T. mcraeensis could shed light on why tyrannosaurs evolved into giants.

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. A formerly unknown relative of the most iconic of all dinosaurs, Tyrannosaurus rex, has been newly identified, according to a study released Thursday. The revelation adds a new clue that could help paleontologists unravel another step in the evolutionary chain that ended with the massive predatory tyrannosaur, T. rex. Called Tyrannosaurus mcraeensis, the creature likely roamed Earth up to 7 million years before T. rex emerged. The bones have been dated to 72 million to 73 million years old during the late Campanian-early Maastrichtian Period. But Tyrannosaurus mcraeensis’ bones were discovered decades before the creature officially got its scientific name. About one-quarter of its fossilized skull was found over the course of the 1980s and early ’90s in an area now known as Elephant Butte, New Mexico. Because of the size of the specimens, the bones were originally categorized by the New Mexico Museum of Natural History & Science as T. rex, which grew up to 39 feet (12 meters) long and 10 tons in weight. There were two big differences between T. rex and T. mcraeensis. “The lower jaw in a Tyrannosaurus rex is actually quite robust. Our jaw is obviously big and toothy, but it’s more slender than what we normally see in a Tyrannosaurus rex,” said Anthony R. Fiorillo, coauthor of the study published Thursday in the journal Scientific Reports. The robust jaw of T. rex meant it “could do whatever it wanted. A more slender jaw, even with the big teeth, means that it would have less bite force.”